A flexographic printing module is described in EP-1 567 340 in applicant's name. The printing module known therefrom is a frame which comprises two opposite frame parts; an anilox roller which is bearing-mounted in the frame in a manner rotatable about an anilox roller axis and extends between the two opposite frame parts; an impression roller which is bearing-mounted in the frame in a manner rotatable about an impression roller axis and extends between the two opposite frame parts; and a plate cylinder assembly. The plate cylinder assembly comprises a stationary shaft; two supporting rings which are each connected with the shaft near an associated end of the shaft; and a plate cylinder which is mounted on the shaft in a manner rotatable about a plate cylinder axis. The diameter of the plate cylinder substantially corresponds to the diameter of the supporting rings. Further, the printing module comprises a first and a second plate cylinder holder assembly which are each connected with an associated frame part, and which are each configured for removably placing and fixing therein a supporting ring of the plate cylinder assembly. In this publication it is not described how on one side the distance and hence the pressure between the anilox roller and the plate cylinder and on the other side the distance and hence the pressure between the impression roller and the plate cylinder can be set.
For the setting problem, EP-1 092 536 A1 provides a solution. In that publication, each plate cylinder holder assembly is provided with two pivotable arms which each provide a support surface for the supporting ring associated with the respective plate cylinder holder assembly. The position of each pivotable arm is settable with a set screw. In total, the known printing module is provided with four independently settable arms, each with an associated set screw.
Also EP-1 285 753 A1 provides a solution to the setting problem. In this publication, as in EP-1 092 536 A1, a system is disclosed which utilizes four slidable or pivotable arms which are each associated with a corresponding set screw. These arms engage the supporting rings of the plate cylinder directly or via a support plate on which the shaft of the plate cylinder rests. The size of the support plate depends on the diameter of the plate cylinder. For each plate cylinder of a defined diameter, in that embodiment, a corresponding support plate is present. Accordingly, such an embodiment involves a set of exchangeable support plates of mutually different dimensions.
The constructions known from EP'753 and EP'536 are complicated and also costly. Moreover, the independent setting of the two distances on either side of the printing module with four set screws is laborious and time consuming. The rear set screws are poorly accessible to the machine operator. As four pivotable arms are employed, the support geometry is not guaranteed, that is, the points of support by which supporting rings abut against the arms may, as a result of improper setting, be set such that the plate cylinder is not positioned centrally between the anilox roller and the impression roller anymore. Such a non-central positioning can have an adverse influence on the printing quality. Since the setting needs to be done accurately for a good printing result, and standstill of the machine leads to production loss and hence additional costs, the proposed solution is susceptible of improvement.
To that end, the invention provides a printing module according to claim 1, in other words, a printing module of the type described above with reference to EP-1 567 340, which is characterized in that each plate cylinder holder assembly comprises a plate-shaped body part which extends in an imaginary body part plane which extends perpendicular to the plate cylinder axis, wherein a side of the plate-shaped body part proximal to the plate cylinder axis forms a supporting ring support surface which extends substantially perpendicular to the body part plane and runs along a curve which extends in the body part plane, wherein the curve is mirror-symmetrical with respect to an imaginary curve symmetry plane which extends substantially perpendicular to the body part plane, and with respect to which the anilox roller axis and impression roller axis are disposed substantially symmetrically, and in which the plate cylinder axis extends. The curve, viewed from the plate cylinder axis, comprises a central concave curve part which is symmetrical with respect to the central curve symmetry plane; a first convex curve part which adjoins a first end of the concave curve part and which extends to a first convex free end; and a second convex curve part which adjoins a second end of the concave curve part and which extends to a second convex free end, wherein the two convex parts are symmetrical with respect to the curve symmetry plane. Further, each plate cylinder holder assembly comprises a body part support assembly via which the body part is connected with the associated frame part, wherein the body part support assembly is configured for pivoting the body part about a first pivoting axis and for pivoting the body part about a second pivoting axis. The first and second pivoting axes are positioned symmetrically on opposite sides of the curve symmetry plane. The first pivoting axis substantially coincides with the impression roller axis, that is, coincides exactly with the impression roller axis or extends parallel to the impression roller axis with the distance between the first pivoting axis and impression roller axis being less than 50 mm. The second pivoting axis substantially coincides with the anilox roller axis, that is, coincides exactly with the anilox roller axis or extends parallel to the anilox roller axis with the distance between the second pivoting axis and anilox roller axis being less than 50 mm.
Owing to the specific pivoting possibility about two pivoting axes and the above-defined positioning of the pivoting axes, it is possible to set the distance between the plate cylinder and the anilox roller without the distance between the plate cylinder and the impression roller being significantly influenced. Consequently, first the distance between the plate cylinder and the anilox roller can be set and then the distance between the plate cylinder and the impression roller. When this latter setting takes place, this does not disturb the previous setting of the distance between the plate cylinder and the anilox roller. Moreover, with the printing module according to the invention it can be guaranteed that the plate cylinder is always substantially centered between the anilox roller and the impression roller. This is because per plate cylinder holder assembly there is only one body part involved whose curve offers two points of support for the associated supporting ring. This is in contrast to the proposal from EP-1 092 536 A1 where for each point of support a separate pivoting arm is provided. Moreover, the printing module according to the invention, as regards the number of construction parts, is simpler and more robust.
The invention further provides a printing machine which is provided with a number of printing modules set up in series behind each other, while at least one of the printing modules is a printing module according to the invention.
Further elaborations of the invention are described in the subclaims and will hereinafter be clarified, on the basis of an exemplary embodiment, with reference to the drawings.
It is noted that the embodiments are not limited to the examples that are shown in the drawings. The drawings serve for clarification only. The embodiments can be employed independently of each other. Also, it is possible that several embodiments of the invention are embodied in a single printing module.